Burgess Shale–type (BST) fossilization of carbonaceous remains
that are ordinarily lost to decay is critical to our understanding of
the early evolution of complex life. Sediment composition, particularly
the abundance of certain clay minerals, has been invoked as a
significant factor in BST fossilization. X-ray diffraction data for 213
Cambrian shales from 19 sedimentary successions on four continents
provide the first comprehensive test of the association of clay mineral
assemblages with BST fossils. Samples containing BST fossils
yield mineralogical compositions that form a subset within the range
represented by samples containing only fossil mineralized skeletons.
Logistic regression and classification tree methods reveal that BST
fossils are more likely to be found in sediments rich in berthierine/chamosite
and poor in celadonite and illite. This characteristic clay
mineralogy probably reflects a high kaolinite/smectite ratio in the
original sediment and enhanced iron availability during early diagenesis.
Models derived from both methods can predict the occurrence
of BST fossils in fossiliferous samples based on clay mineralogy
with ~80% accuracy, providing a mineralogical signature that may
be useful in refining the search for BST fossils on Earth and beyond.